Humans now consume more of Earth's natural resources than the planet can replace, raising doubts about the long-range sustainability of modern economies, according to a new study being published in The Proceedings of the National Academy of Sciences.
For the past 20 years, people have been depleting natural resources, including fish, forests and arable land, at a rapid rate. Economic expansion has boosted demand for resources and overshot the planet's ability to regenerate goods and services by 20 percent, the study says.
"You can overdraw on nature's accounts and leave a debt. We are no longer living off nature's interest, but nature's capital. Sustainable economies are not possible if we live beyond the means of nature," said Mathis Wackernagel, lead author of the study and sustainability program director for Oakland-based Redefining Progress.
The study, titled "Tracking the Ecological Overshoot of the Human Economy," was produced by an international team of researchers. It marks the first attempt to build a comprehensive accounting method to assess the cost borne by nature by human activity.
The latest study is part of a growing body of work that attempts to calculate the cost to the environment of human activities, not just the value of a product in a marketplace.
In estimating the "ecological footprint" of humanity, the authors looked at six activities over the past 40 years, calculated how much land and biological production is devoted to those activities and how much is needed to sustain them.
The researchers looked at growing crops for food and other products; grazing animals for meat, milk and wool; logging; fishing; providing space and materials for houses, highways, dams and industries; and fossil fuel burning.
According to their analysis, human demand has been outstripping nature's ability to resupply since the early 1980s. Since 1961, the human demand on resources has nearly doubled and today exceeds Earth's replacement capacity by 20 percent, the researchers found.
Much of the impact is in the area of fossil fuel use.
Eleven researchers from England, Austria, Mexico, Norway, Switzerland and the United States participated in the study.